The long-range goal of the research described in this project is to make use of in vivo systems define the biochemical-molecular mechanisms that regulate (i) the expression of proteins that promote the transition of the uterus from a state of quiescence to one of preparedness for labor (uterine phase I of parturition); (ii) the components of the endothelin (ET)/enkephalinase-parathyroid hormone-related protein (PTH-Rp) system of the uterus and the amnion-chorionic vessels; and (iii) the gene-specific antiprogestin action of transforming growth factor-beta (TGF-beta) and other peptides on the uterus. We will use human myometrial cells in culture to investigate the regulation of expression of proteins in myometrium that we believe contribute to uterine preparedness for labor: viz., oxytocin receptor, connexin43, TGF-beta1 & TGF-beta3, PTH-Rp, and calbindin-9K. Having identified regulators of the synthesis of functional phase 1 proteins, we will evaluate the effects of selected uterine phase 1 proteins, e.g., TGF-beta1 and PTH-Rp, on the expression of other phase 1 proteins in myometrial cells. We will define the mechanisms that govern ET biosynthesis, processing, action, and enzymatic degradation (by enkephalinase) in uterine and extraembryonic fetal tissues. We present evidence in support of the possibility that there is a unique form of progesterone withdrawal in myometrium in human pregnancy. This putative mechanism can operate without a decline in the levels of plasma or cellular progesterone or a change in progesterone receptor number or function. Progesterone action is negated in selected cells (namely, myometrial smooth muscle an decidua) in a gene-specific manner in vitro by TGF-beta, viz., TGF-beta acts in these cells in culture to oppose the effects of progestin on the synthesis of 4 different proteins, i.e., PTH- Rp, enkephalinase, ET-1, and connexin43. The genes/proteins affected by TGF-beta are exemplary, we believe, of those involved either in a regulatory or a functional capacity, or both, in the transition of myometrium from a state of quiescence to one of preparedness for labor; and importantly, TGF-beta1 MRNA in myometrium increases strikingly late in human pregnancy. The products of the genes affected by TGF-beta also are components of the fetal membrane-chorionic vessel ET-1/enkephalinase-PTH-Rp system to which we refer. We will define the mechanism(s) that accounts for the gene-specific, antiprogestogenic actions of TGF-beta (and other agents); we will identify the source(s) of TGF-beta available to myometrium in late pregnancy, i.e., potential sites of synthesis and/or activation of latent TGF-beta. Namely, we will define the cells in which TGF-beta is synthesized and those in which latent TGF-beta is converted to active TGF- beta for action in myometrial cells. We will use monolayer cultures of human cells that we have characterized as model systems. We speculate that steps to modify the commencement or progression of phase I processes could serve to arrest or prevent preterm labor.